Workpiece supports for supporting workpiece from underneath have been provided for cutting workpiece and the like, and the present applicant has also proposed and submitted patent applications for various workpiece supports (Japanese Patent Application Nos. H11-46922, 2000-84112, and others).
The workpiece support in Japanese Patent Application No. H11-46922 has a case member, a rod, a rod-moving hydraulic cylinder, a sleeve body, a pressure intensifier, an outer peripheral hydraulic chamber, and the like.
The sleeve body is configured so as to be capable of elastic deformation and is supported by the case member, the rod is fitted movably into the sleeve body, and the external peripheral hydraulic chamber is formed on the external periphery of the sleeve body. The pressure intensifier and the rod-driving hydraulic cylinder are built into the case member, and a configuration is adopted whereby oil pressure from an oil pressure supply port formed in the case member is simultaneously supplied to the pressure intensifier and the rod-driving hydraulic cylinder.
In other words, as the rod-driving hydraulic cylinder is actuated by oil pressure supplied via the oil pressure supply port and the rod is moved in the workpiece-supporting direction, the pressure intensifier is actuated and caused to generate high oil pressure in the external peripheral hydraulic chamber, the thin-walled cylinder of the sleeve body is elastically deformed by the high oil pressure so as to shrink in diameter, and the rod is locked.
However, in this workpiece support,because oil pressure is supplied from a shared oil pressure supply port simultaneously to the pressure intensifier and the rod-driving hydraulic cylinder, the rod tends to lock before making contact with the workpiece, thus creating drawbacks of inadequate dependability and reliability of the operation of the workpiece support.
The workpiece support in Japanese Patent Application No. 2000-84112 has a case member, rod, rod-driving hydraulic cylinder, sleeve body, pressure intensifier, and external peripheral hydraulic chamber, as well as a restrictor valve(throttle valve) provided in the oil supply passage leading from the oil pressure supply port to the input oil chamber of the pressure intensifier, and a non-return valve that is capable of discharging the oil pressure of the input oil chamber in the discharge oil passage leading from the input oil chamber to the oil supply port, and that opens from the oil supply port when oil pressure is discharged.
Because a restrictor valve is placed in the oil supply passage leading from the oil pressure supply port to the input oil chamber in this workpiece support, the pressure intensifier can be made to operate subsequently to the rod-driving hydraulic cylinder, and thus the rod can be locked after coming in contact with the workpiece. However, this arrangement has drawbacks because the need for providing a restricting valve and non-return valve increases the number of parts and complicates the structure.
An object of the present invention is to simplify the structure of a workpiece support and increase the dependability and reliability of its operation.